Chapter 3. Operators

Describes the built-in operators available in Postgres.

Postgres provides a large number of built-in operators on system types. These operators are declared in the system catalog pg_operator. Every entry in pg_operator includes the name of the procedure that implements the operator and the class OIDs of the input and output types.

To view all variations of the "||" string concatenation operator, try

    SELECT oprleft, oprright, oprresult, oprcode
    FROM pg_operator WHERE oprname = '||';

oprleft|oprright|oprresult|oprcode
-------+--------+---------+-------
     25|      25|       25|textcat
   1042|    1042|     1042|textcat
   1043|    1043|     1043|textcat
(3 rows)
   

Users may invoke operators using the operator name, as in:

select * from emp where salary < 40000;
   

Alternatively, users may call the functions that implement the operators directly. In this case, the query above would be expressed as:

select * from emp where int4lt(salary, 40000);
   

psql has a command (\dd) to show these operators.